Memorabilia are objects that are treasured for their memories and valued for connections to historical events, culture, or entertainment. Such memorabilia items include sports equipment, garments, photographs, trading cards, programs, posters, brochures, media clippings, buttons, pennants, stickers, certificates, documents, souvenirs, musical instruments, autographs, letters, journals, diaries, entertainment-related merchandise, movie memorabilia, and other, often-licensed, sold or exchanged items. As memorabilia sales and auctions grew into extensive businesses, authentication services developed to address memorabilia collectors' concerns about purchasing counterfeit memorabilia items. Some authentication services send witnesses to authentication events, such as a gathering for professional athletes to autograph sports equipment they used during sporting events. The witnesses can issue certificates of authenticity, mark the memorabilia items with invisible ink, and place special stickers on memorabilia items. However, unscrupulous memorabilia dealers can duplicate the certificates, markings, and stickers, thereby flooding the market with counterfeit items. Memorabilia collectors may lose significant amounts of their investments by inadvertently purchasing counterfeit items and by having the value of their authentic items decline due to general market uncertainty over authenticity.